Subsurface safety valves are used in wells for emergency shutoff. Typically they are a part of the tubing string and are operated by a hydraulic system at the surface that provides pressure to a control line that runs from the surface to the valve housing. The valve housing connection communicates with an operating piston that is connected to a flow tube. A flapper is biased toward a seat (schematically illustrated as 31 in FIG. 1) by a torsion spring on the flapper pivot shaft. The movement of the flow tube under pressure delivered through the control line which moves the operating piston connected to it results in pivoting the flapper behind the flow tube. This defines the valve open position. The valve closed position has the flow tube moved up under the force of a spring when pressure in the control line is removed.
When the flapper is closed, a large pressure differential can build up across it. The need to equalize that pressure across the flapper before trying to move the flapper off the seat has been recognized and equalizer valves in the flapper have been in use for some time. One early example of this concept is U.S. Pat. No. 4,478,286. Later examples are U.S. Pat. Nos. 6,644,408 and 7,204,313.
Shape memory alloys (SMA) and materials that assume their original dimensions in response to a stimulus have been used as actuating members to move the ultimate valve member between open and closed positions. Some examples of this design can be seen in U.S. Pat. Nos. 5,199,497; 6,840,257 and 7,055,793.
Prior subsurface safety valve designs mentioned above have used the flow tube to actuate the equalizer valve. There has generally been enough power to do this with operating pistons that are driven hydraulically from the surface through a control line. More recently electrically operated subsurface safety valves are being developed where there are concerns about generating enough force to displace an equalizer valve with the flow tube. The present invention addresses this issue with a valve member made of SMA or another material that can seal a flapper passage in the run in configuration and can be triggered to assume a different shape that allows equalization of pressure. The operation is envisioned to be independent of a flow tube. Some of the designs being developed may not even use a flow tube. These and other aspects of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings with the understanding that the claims determine the full scope of the invention.